Gardening Columns

Isn't it a miracle that such lovely poppies grow from tiny poppy seeds?

The Wonder of Seeds

First published on garden.org on February 16, 2006, by Suzanne DeJohn

Over the years, I've started thousands of seeds indoors in preparation for the coming growing season. Yet the miracle of seeds never fails to astound me. How can a tiny, inert, rock-hard nugget be so quickly transformed into a lush, green plant? How can that tiny seed contain all the information it needs to grow? The biology of seeds isn't just fascinating, however, it is also important for gardeners planning to start their own seeds.

Are Seeds Alive?
Teachers will sometimes spark classroom debate by asking students, "Are seeds alive?" Even "grown-ups," however, have trouble answering this question. Scientists avoid having to give a yes-or-no answer by providing a third alternative: Seeds are neither alive nor dead, but instead are dormant. Although they show no signs of metabolic activity, a commonly used indicator of the presence of life, viable seeds contain everything they need to burst forth and grow. But until they are exposed to the proper environmental conditions, they remain in a state of rest.

Easy to Grow
We expect the seeds in the packets we purchase to germinate and grow with relative ease, and rightly so. Commercially available seeds have been chosen or bred for that characteristic. Although we occasionally come across plants whose seeds are described as "challenging" to germinate, most of the seeds we buy are reliable germinators. Wild plants, on the other hand, have evolved remarkable adaptations to maximize the chances of their seeds' survival -- and easy germination isn't always one of them.

Seeds in Nature
If you think about the role of seeds in nature, the miracle contained in that packet of seeds becomes even more amazing. Seeds are compact genetic storage structures that allow plant species to endure harsh conditions that render growth impossible. Depending upon the plant's native habitat -- the environment in which it evolved -- these unfavorable conditions might be extreme cold, heat, or perhaps drought. Seeds carry the genetic information that not only enables germination, but also instructs the seeds when not to germinate.

For example, plants that evolved in regions with long, cold winters often produce seeds that sit dormant over the winter, then sprout to life in the spring. Why don't those seeds germinate during a warm spell in autumn?

Seed Pretreatments: Chilling
Seeds from many temperate plants evolved the survival mechanism of requiring an extended period of chilling before they will germinate. If you have ever tried to start seeds of lavender, primula, or delphinium, you probably know about prechilling, or "stratifying," seeds. To get these seeds to germinate, you must mimic the conditions they would face outdoors; that is, you must expose them to moist, cool conditions for an extended period. This is usually best accomplished by sowing the seeds in a flat of moist seed-starting mix, placing the flat in a plastic bag, and storing the bag in the refrigerator for the specified period of time.

Tough Seed Coats
Some seeds have especially tough seed coats, making them impervious to water and therefore slow to germinate. Why might seeds have evolved this feature? Consider that most seeds grow best when buried in soil, as opposed to simply laying on the surface. Buried roots are much less likely to dry out or be baked in the sun. In nature, the germination-inhibiting hard seed coats of some seeds are breached only when the seeds have been exposed to the grinding action of soil particles as they are washed into the soil during a heavy rain. Others must be exposed to soil fungi and bacteria that decompose their seed coats. Nature has devised a way to keep some seeds from germinating until they are "planted."

Certain plants have evolved such that their seeds germinate only after exposure to the acidic environment of a bird's gut. These seeds often occur inside tasty fruits; birds eat the fruits and pass the seeds, along with a ready source of fertilizer!

Gardeners deal with the tough seed coats of morning glory and sweet pea seeds by soaking or scarifying. Soaking means placing seeds in warm water for a prescribed length of time. Scarifying means making a hole in the seed coat by nicking each seed with a file or a pin so it can absorb water. To scarify larger quantities of seeds, line a can with a coarse grade of sandpaper, then place the seeds in it and shake it until the seeds are scratched.

Some Seeds Need Light
Why do some seeds need light to germinate? Once again, nature gives us clues. Consider a seed that's fallen in a dense grove of trees. Would it have much chance to grow and compete in that environment, with little light, and competition for water from all those tree roots? Now consider the same seed, planted in an open field, with plenty of light and water. Maybe the seed was carried there by a bird or animal. Or perhaps a windstorm knocked down a tree in the grove, opening up a patch of ground to the sunlight. Now that little seed has a fighting chance to grow. If you are sowing seeds that require light to germinate, simply press them into the soil surface, and leave the seed tray exposed to light.

Trial by Fire
Finally, some seeds, such as those of chaparral-type plants growing in regions exposed to frequent lightning storms, require exposure to fire in order to germinate. Fortunately, I don't know of any common garden plant that requires gardeners to go to this extreme!

As you start your seeds this spring, take a moment to ponder the miracle of seeds and the wonders of a natural world that has produced such fascinating little packages waiting to burst forth with life.